Method and apparatus for automatic multi-run welding

Abstract

In automatic multi-run welding of a butt joint (37), for example a V-type joint, U-type joint, a sensor (44) oscillating transverse to the weld joint scans at several joint portions (F1, F2) a number of points (41, 41a, 41b etc.) on the contour of the joint. The coordinates of the points are determined for two directions, preferably in the vertical direction and lateral direction of the joint. The points are corner points of a polygon whose area is nearly identical to the cross-sectional area of the joint. Welding parameters, for example the welding speed, which control the amount of welding material per unit of length in a bead to be deposited in the joint are determined for the different joint portions (F1, F2) as a function of the corresponding polygon area. By virtue of the adaptation of the parameters to the varying joint cross-section, the joint is filled uniformly despite deviations in the shape of the joint from the ideal shape. Moreover, these polygon areas are used to determine the required number of beads per layer and the condition for deposition of a top layer with which the welding is finished.

What is claimed is: 
     
       1. A method for automatic multi-run welding of a joint formed between at least two adjacent pieces to be welded by a weld head to form a weld, said welding comprising feeding a solid welding material into the weld at a speed of feed while moving at least one of the weld head and the two adjacent pieces relative to the other of the weld head and the two adjacent pieces at a relative speed of movement, each of the at least two adjacent pieces comprising a joint surface, each joint surface being disposed for being welded to at least one adjacent joint surface, said method comprising the steps of: scanning at least a cross-section of at least a portion of the joint with scanning means;   depositing at least a first bead of solid welding material along said at least a portion of the joint;   directly measuring by said scanning a plurality of actual points on the joint surfaces of said at least a portion of the joint;   generating data corresponding to coordinates of said plurality of actual points;   calculating with said data to obtain values to determine at least a cross-sectional area of said at least a portion of the joint;   calculating a cross-sectional area of the at least a first bead of solid welding material deposited along said at least a portion of the joint;   calculating a residual area for said at least a portion of the joint, said residual area being the different between said calculated cross-sectional area of said at least a portion of the joint and said calculated cross-sectional area of the at least a first bead of solid welding material deposited along said at least a portion of the joint;   depositing at least a second bead of solid welding material along said at least a portion of the joint;   calculating at least one of: said speed of feed of the solid welding material being fed into the weld for said at least a portion of the joint as a function of said residual area of said at least a portion of the joint; and   said relative speed of movement between the weld head and the two adjacent pieces for said at least a portion of the joint as a function of said residual area of said at least a portion of the joint; for said depositing of the at least a second bead of solid welding material along said at least a portion of the joint.       
     
     
       2. The method for automatic multi-run welding of a joint according to claim 1, wherein said sensor means is mounted in front of the solid welding material for scanning said at least a portion of the joint before said at least a portion of the joint is welded. 
     
     
       3. The method for automatic multi-run welding of a joint according to claim 2, wherein each of said at least two adjacent pieces comprises a top surface substantially transverse to the joint surface, and said method further comprises: obtaining at least one coordinate of at least one point on the at least one top surface, said at least one point on the at least one top surface being in proximity of an intersection of the at least one top surface and the joint surface;   calculating a plane defined by the at least one top surface by using said at least one coordinate of said at least one point;   calculating a line between at least two of said plurality of points on the joint surface; and   determining a point of intersection of said line with said plane of the at least one top surface, said point of intersection defining an edge point of an edge of the joint at the intersection of the at least one top surface and the joint surface.   
     
     
       4. The method for automatic multi-run welding of a joint according to claim 3, wherein: said first bead of solid welding material comprises a fixed amount of solid welding material per unit length of the joint.   
     
     
       5. The method according to claim 4, wherein said at least one portion of the joint comprises a plurality of portions of the joint, and said method further comprises the steps of: depositing said first bead of solid welding material along each of said plurality of portions of the joint;   continuously scanning the joint with said sensor during said depositing of said first bead of solid welding material to directly measure a plurality of points in each said portion of the joint;   calculating a residual area for each said portion of the joint;   depositing the at least a second bead of solid welding material along each said portion of the joint; and   calculating at least one of: said speed of feed of the solid welding material being fed into the weld for each said portion of the joint as a function of said residual area of said portion of the joint; and   said relative speed of movement between the weld head and the two adjacent pieces for each said portion of the joint as a function of said residual area of said portion of the joint; for said depositing of the at least a second bead of solid welding material along each said portion of the joint.       
     
     
       6. The method for automatic multi-run welding of a joint according to claim 5, further including: (a) using only one of: said speed of feed of a solid welding material being fed into the weld, and   said relative speed of movement between the weld head and the at least two adjacent pieces, as a welding parameter to control the welding in said at least a portion of the joint; and       (b) using the same said welding parameter of step a) to control the welding in each portion of the joint.   
     
     
       7. The method for automatic multi-run welding of a joint according to claim 6, wherein said one welding parameter to control the welding is said relative speed of movement between the weld head and the at least two adjacent pieces. 
     
     
       8. The method for automatic multi-run welding of a joint according to claim 7, further including: calculating an average cross-sectional area for the joint from each said cross-sectional area of each portion of the joint;   calculating an average relative speed of movement between the weld head and the at least two adjacent pieces for the joint, said average relative speed being a function of said average cross-sectional area: and   calculating a relative speed of movement for each portion of the joint as a function of the ratio between said cross-sectional area for the joint portion and said average cross-sectional area: and   determining a range of speeds for said relative speed of movement between the weld head and the at least two pieces, said range of speeds comprising a maximum speed above said average relative speed of movement and a minimum speed below said average relative speed of movement.   
     
     
       9. The method for automatic multi-run welding of a joint according to claim 8, further comprising producing a warning signal upon said relative speed of movement at least one of: exceeding said maximum speed, and   falling below said minimum speed.   
     
     
       10. The method for automatic multi-run welding of a joint according to claim 9, wherein said relative speed of movement for each joint portion is a function of said residual area calculated for the joint portion and said relative speed of movement for each of a preceding joint portion and a following joint portion; and a transition between a first relative speed of movement in a first joint portion and a second relative speed of movement in a second joint portion adjoining the first joint portion is effected gradually when said second relative speed of movement is at least one of: greater than and less than said first relative speed of movement.   
     
     
       11. The method for automatic multi-run welding of a joint according to claim 10, further comprising: determining a width of each portion of the joint at the base of the portion of the joint;   calculating a width value for each portion of the joint, said width value being equal to k·b 1 , in which k is a factor with a predetermined value between 0.5 and 1.0 and b 1  is the width of each portion, and   calculating an average width value of the joint from the width values of each of the joint portions.   
     
     
       12. The method for automatic multi-run welding of a joint according to claim 11, further including depositing additional beads of solid welding material along the joint to form at least one intermediate layer of beads of weld material, the additional bead being deposited being: alongside a previous bead of solid welding material when the average width of the joint is greater than a predetermined value,   on top of a previous bead of solid welding material when the average width of the joint is less than a predetermined value, and   on top of a previous bead of solid welding material when the average width of the joint is equal to a predetermined value.   
     
     
       13. The method for automatic multi-run welding of a joint according to claim 12, wherein said plurality of points for each portion of the joint define a polygon; said polygon being further subdivided into a first and a second subpolygon by a centerline through the joint;   each said subpolygon comprising the measured points on each respective joint surface and joint edge.   
     
     
       14. The method for automatic multi-run welding of a joint according to claim 13, further including: calculating a cross-sectional area area of each said subpolygon;   calculating a cross-sectional area of a last-deposited bead of welding material:   determining said welding parameters for depositing a bead of solid welding material against a joint surface of a subpolygon as a function of the subpolygon area and of the cross-sectional area of a last-deposited bead in an underlying layer.   
     
     
       15. The method for automatic multi-run welding of a joint according to claim 14, further including: determining the width (b 2 )of said intermediate layer of beads of weld material;   depositing a first bead of weld material along one joint surface of the joint;   determining a cross-sectional area (a 1 ) of the first deposited bead of weld material:   determining a height of the first deposited bead of weld material in said intermediate layer for each portion of the joint;   calculating a mean value (h 1 ) for said height of the first deposited bead of weld material;   depositing a second bead of weld material along a second joint surface of the joint:   determining a cross-sectional area (a 2 ) of the second deposited bead of weld material;   calculating a height of said second deposited bead of weld material using the equation -h 2  =(h 1  ·a 2 )/2   calculating an average height value (h) for the first and the second deposited beads of weld material by using the equation -h=(h 1  +h 2 )/2; and   calculating an average area value for the cross-sectional area of said intermediate layer as a function of the product of said width of said intermediate layer and said average height value.   
     
     
       16. The method for automatic multi-run welding of a joint according to claim 15, further including: depositing at least three beads of weld material in said intermediate layer when said average area value is greater than a predetermined value;   calculating a number of beads (Z) of weld material to be deposited in said intermediate layer by using the equation -Z=2·b 2  h/(a 1  +a 2 ) and rounding off the resultant value of Z to the nearest integer value:   determining a number of additional beads of weld material to be deposited between the first and the second beads of weld material deposited along the joint surfaces;   determining a cross-sectional area needed for each additional bead of weld material to be deposited between the first and the second beads of weld material by interpolation with respect to the cross-sectional areas a 1  and a 2  of the first and the second beads of weld material deposited along the joint surfaces, and   depositing the additional beads of weld material in said intermediate layer between the first and the second beads of weld material at a relative speed of movement which is inversely proportional to the cross-sectional area of the additional beads of weld material.   
     
     
       17. The method for automatic multi-run welding of a joint according to claim 16, further comprising, before the deposition of a layer: calculating a residual area (R pn ) in each portion of the joint for each layer when the layer is to receive more than two beads of weld material:   calculating an average residual area (R pm ) for each layer from each of said calculated residual areas:   calculating an average relative speed of movement (V pm ) as a function of said average residual area:   calculating a residual area (R pn1  and R pn2 ) for each of said first subpolygon and said second subpolygon; and   calculating the relative speed of movement for the deposition of the first and second beads of weld material by using the equations:   V.sub.pn1 =(V.sub.pm ·R.sub.pm)/2R.sub.pn1 and V.sub.pn2 =(V.sub.pm ·R.sub.pm)/2R.sub.pn2.       
     
     
       18. The method for automatic multi-run welding of a joint according to claim 16, further comprising: calculating a quotient for each portion of the joint in a last-deposited intermediate layer from the average residual area of each portion of the joint in the last-deposited intermediate layer and said average area value of the cross-sectional area in each portion of the joint in the last-deposited intermediate layer; and   depositing a top layer of beads of weld material in the joint on the last-deposited intermediate layer when said quotient is less than a predetermined value, the top layer of beads of weld material containing one more bead of weld material than the last-deposited intermediate layer.   
     
     
       19. Apparatus for automatic multi-run welding of a joint formed between at least two adjacent pieces to be welded by a weld head to form a weld, each of the at least two adjacent pieces comprising a joint surface, each joint surface being disposed for being welded to at least one adjacent joint surface, said apparatus comprising: a welding housing;   a weld head disposed on the welding housing, the weld head comprising means for receiving a solid welding medium and means for feeding the solid welding medium to the weld;   a welding power supply for providing current for the weld head;   means for providing relative movement between the weld head and the at least two adjacent pieces;   sensor means for scanning at least a portion of the joint, said sensor means being for directly measuring a plurality of actual points on at least one joint surface to generate data corresponding to coordinates of said points;   processing means for receiving said data corresponding to coordinates of said points, for calculating a cross-sectional area of the joint from said data corresponding to coordinates of said points, for calculating a cross-sectional area of a deposited bead of welding material, for calculating a residual area for the joint, said residual area being the difference between said calculated cross-sectional area of the joint and said calculated cross-sectional area of the deposited bead of welding material, for calculating at least one of: a speed of feed of the solid welding medium into the weld, and   a relative speed of movement between the weld head and the at least two adjacent pieces,      and for producing signals for control of the welding; and   control means for receiving said signals for control of the welding, and for controlling at least one of: said means for controlling the means for feeding the weld rod to control the amount of solid welding material being fed into the weld as a function of the residual cross-sectional area, and   said means for controlling the means for providing relative movement between the weld head and the at least two pieces to control the amount of solid welding material being deposited along the joint as a function of the residual cross-sectional area.     
     
     
       20. The apparatus for automatic multi-run welding of a joint according to claim 19, wherein said sensor means is mounted in front of the weld head for scanning at least a portion of the joint before the welding of at least a portion of the joint.